This project examines the molecular basis of the interaction of fibronectin with cells. Fibronectin has become a prototype for adhesive proteins because of the vast amount of knowledge that has been gathered on this protein. Detailed information on fibronectin will therefore give insight to a multitude of biological phenomena in which cellular adhesion plays a role, including the metastatic spread of tumor cells. Synthetic peptides modeled after the amino acid sequence of the cell attachment site of fibronectin have been used to show that the recognition site for cells is a four amino acid sequence, arg-gly-asp-ser. Peptides containing this sequence promote cell attachment when coupled to a surface and inhibit cell attachment when used in a soluble form. Synthetic peptides in which any of the three amino acids has been substituted--even if a closely related amino acid is used for the substitution--are inactive, suggesting that a point mutation in the fibronectin gene could give a fibronectin defective in the cell attachment function. In the future we will use the synthetic peptides as probes to determine the chemical nature of the cell surface component(s) ("receptor") that interacts with fibronectin to induce cell attachment and to study the role of fibronectin in various cell culture and differentiation systems. The DNA clones that correspond to the cell attachment domain of fibronectin cross-hybridize with several restriction fragments from genomic DNA. DNA cloning corresponding to these genomic sequences, which represent the fibronectin gene and possibly genes for proteins related to fibronectin, will be isolated and characterized. If genes of proteins with sequences related to fibronectin are found, the proteins will be identified and characterized. Malignant cells often lack cell surface fibronectin and other extracellular matrix components, but another adhesive protein, vitronectin, is retained at their surface. The role of this cell surface vitronectin in endowing transformed cells with their aberrant growth and adhesive properties will be studied by determining the orientation, adhesive activity, and expression of vitronectin at the surface of the characteristics that most consistently accompany malignancy; and since such changes appear to relate to the invasiveness of tumor cells, these studies will increase the understanding of a very significant aspect of malignancy. (V)